Many existing systems and methods for detecting biological substances in a sample have disadvantages that make them unsuitable for use in many settings. Some of the known problems associated with current detection devices include their complexity, lack of sensitivity and/or specificity, and high cost. The detection of Methicillin-resistant Staphylococcus aureus (“MRSA”) infection presents particular difficulty chiefly due to its similarity to more common strains of Staphylococcus aureus (“Staph aureus”). The ability to reliably distinguish MRSA from other forms of Staph aureus currently requires very precise and labor-intensive detection methods. For example, the CHROMagar™ test, which is used in 85-90% of current MRSA screens, involves placing a sample on a growth medium that is inoculated with a set amount of antibiotic. The growth medium is configured to impart a specific color to any type of Staph aureus colonies. If the appropriately colored bacteria are found growing on a specific portion of the plate, it is assumed that they must be MRSA due to their resistance to the antibiotic. The accurate interpretation of this test requires skilled subjective assessment of the color and growth pattern of cultivated samples. Further, the set amount of antibiotic may not be appropriate for all levels of MRSA infection, causing inaccurate test results in some cases. Other methods of MRSA detection, such as DNA-based detection, are expensive, i.e., $40 to $50 per test, and requiring a roughly $50,000 detection instrument; or, like the CHROMagar test, rely on the subjective interpretation skills of a user. Thus, there is a need for cost-effective, easy to use and accurate systems, methods and devices for analyzing biological samples for the presence of MRSA.
While detection of MRSA by chemiluminesent device, which is powered by a sensor integrated chip (“Sensor IC”), has the potential to address many of these problems, previous attempts to do so have failed. First, there is the difficulty of detecting MRSA itself. MRSA's similarity to other, less treatment-resistant forms of Staph aureus require the use of a specific biological capture agent. Further, MRSA is frequently present in the bodies of individuals without causing an infection, and therefore it is necessary to identify a detectible analyte that is indicative of an infection caused by MRSA. Accordingly, MRSA Penicillin Binding Protein 2a, which directly responsible for MRSA's resistance to antibiotic treatments, is a preferable analyte showing that a MRSA infection was actually established in the body.
In addition to selection of the proper analyte, previous attempts failed because of a lack of appreciation for the complexity of sample preparation necessary to use a chemiluminescent device. Previous methods did not address the development of room temperature stable formulations of reagents and capture antibodies necessary to simply and reliably extract the PBP2a and capture it for testing.
Previous methods also relied on manual application to the test strip of a luminous reagent, which is extremely difficult to meter with the necessary precision. Lack of consideration of the microfluidic challenges of the method also hindered the ability to ensure the proper speed and direction of sample and reagent flow across the reaction zone. In addition, previous Sensor IC systems, because of the extreme sensitivity of the detection device, were not robust. Namely, slight variations in technique by a user, or movement of the system caused insufficiently precise sample alignment with the Sensor IC diodes, and hence erroneous results. Significant improvements in the cassette device latching system and electromagnetic radiation apertures, as well as improvements to the cassette handler design were necessary to provide the necessary robustness to make a chemiluminescent system a viable testing platform. Finally, previous Sensor IC detectors did not provide diode calibration to ensure the needed accuracy to read a MRSA sample. Therefore the development of components and algorithms designed to calibrate the diodes was necessary to create a working system.
Before continuing with the background, a variety of definitions should be made, these definitions gaining further appreciation and scope in the detailed description and embodiments of the present invention.